The present disclosure relates to filter circuits, and in particular although not necessarily, ripple current reduction filter circuits.
LED lamps that are connected to a mains electricity supply may need to comply with various regulations. One such regulation is for example the Energystar requirement that lamps with an input power >5 W must have a power factor (PF) >0.7. Another example is IEC61000-3-2 that sets tight limits to the harmonic distortion of the input current for lamps consuming more than 25 W. Having a power factor close to unity and a total harmonic distortion below a few percent can imply that the input current has almost the same shape as, and is in phase with, the waveform of the mains input voltage. Other requirements can address the quality of light, for example by demanding a low amplitude of the ripple in the intensity of the radiated light. As is known in the art, “ripple” is an unwanted residual periodic variation of a direct current (DC) waveform.
These requirements in terms of having both (i) a high power factor, and (ii) a low output ripple have consequences for the design of LED drivers.